Catalysts for the hydrotreatment of hydrocarbons and use thereof in the reforming and isomerization of hydrocarbons in the presence of hydrogen

ABSTRACT

These catalysts comprise: A refractory oxide-mineral carrier; a halogen element, present in combined form; and, in free or combined form, 
     (a) a platinum-group metal, m1 
     (b) tin, 
     and additionally a metal, M1, from groups Ia and IIa of the periodic table of the elements in such an amount that: 0.2≦M2/M1≦10. 
     Specifically, said metal from groups Ia and IIa may be sodium, lithium, potassium, calcium or barium.

The present invention relates to novel catalysts for the hydrotreatmentof hydrocarbons. It further relates to the use of said catalysts in thereforming and isomerization of hydrocarbons in the presence of hydrogen.

By catalytic hydrotreating processes are meant treatments to whichhydrocarbon charges are subjected in the presence of hydrogen and of acatalyst and which involve, separately or concurrently, hydrogenation,dehydrogenation, isomerization, cyclization, dehydrocyclization andaromatization reactions.

One example of a process in which these reactions occur concurrently iscatalytic hydroreforming, a process which is employed particularly intreating petroleum fractions intended for the manufacture of gasolinesin order to increase the octane number of these fractions. This processhas come into wide use as a result of the present demand for motor-fuelgasoline. Moreover, the current trend toward the reduction ofatmospheric pollution caused by automotive vehicles calls for theproduction of gasolines which can be used "as is", without the additionof tetraethyllead, to increase the octane rating.

In catalytic hydroreforming, the operating conditions are selected sothat cracking reactions are minimized and the dehydrocyclization,dehydrogenation and isomerization reactions are promoted.

Particularly when paraffins and naphthenes are used as feedstock, thedehydrocyclization and dehydrogenation reaction, respectively, resultsin the formation of aromatic hydrocarbons which, apart from being ofinterest as fuels because of their high octane number, are suited foruse as raw materials in the petrochemical industry.

Another example of a catalytic hydrotreating process is the process forisomerization of hydrocarbons. This process may be employed particularlywith aromatic and saturated or olefinic aliphatic hydrocarbons. Forexample, it may be used with aromatic hydrocarbons to increase theproduction of paraxylene, which is of particular interest as a rawmaterial in the manufacture of polyesters.

The most widely used catalysts are those which contain a platinum-groupmetal, usually platinum, supported on a refractory oxide mineral oflarge specific surface, such as alumina. Bi- or trimetallic catalysts,which have improved properties, such as higher stability, have come intouse.

Thus, catalysts containing tin and platinum are known. For example,French Pat. No. 2,031,984 and the addition thereto, U.S. Pat. No.2,130,881, which are owned by the applicants' assignee describecatalysts containing platinum and, optionally, iridium, as well as atleast one element from the group consisting of lead, tin and germanium.

Catalysts containing platinum, tin and metals from group Ia or IIa arefurther known from U.S. Pat. Nos. 3,851,003, 3,909,451 and 3,998,900. Inthe examples described in these patents, the catalysts always have aratio M2/M₁ (number of atoms of a metal M2 from group Ia or IIa tonumber of atoms of a metal M1 from the platinum group) greater than 10.These catalysts are used primarily in the dehydrogenation of saturatedaliphatic hydrocarbons. Said patents indicate (see column 3, line 63 etseq., of U.S. Pat. No. 3,851,003, for example) that the presence of analkali or alkaline-earth metal diminishes the isomerization andaromatization reactions.

The applicants have found that it is possible to increase, in ahydroreforming process, the yield, particularly of aromatichydrocarbons, which makes for a high-octane fuel, by using catalystswhich in addition to a platinum-group metal and tin contain at least onemetal selected from the group consisting of the metals of groups Ia andIIa of the periodic table of the elements and have an M2/M1 ratio notover 10, these catalysts being also suited for use in the isomerizationof alkylaromatic hydrocarbons.

The present invention thus proposes catalysts which on the one hand makeit possible to obtain improved yields of effluents having a very goodoctane number and, on the other hand, lend themselves to theisomerization of alkylaromatic hydrocarbons.

To this end, the present invention has as a first preferred embodimentcatalysts for the hydrotreatment of hydrocarbons which comprise

a refractory oxide-mineral carrier;

a halogen element, present in combined form; and,

in free or combined form,

(a) from 0.02 to 2% and preferably from 0.10 to 0.70%, based on thetotal weight of the catalyst, of at least one metal M1 from the platinumgroup, and

(b) from 0.02 to 2%, and preferably from 0.05 to 0.60%, based on thetotal catalyst weight, of tin,

said catalysts being characterized in that they contain, in combinedform, at least one metal M2 selected from groups Ia and IIa of theperiodic table of the elements in such an amount that the ratio M2/M1 ofthe number of atoms of the metal M2 to the number of atoms of the metalM1 is such that 0.2≦M2/M1≦10 and, preferably, 0.5≦M2/M1≦5.

Under this definition of the invention and throughout this application,the term "platinum-group metal" means one of the following metals:Ruthenium, rhodium, palladium, osmium, iridium, and platinum.

The invention relates more particularly to catalysts as defined abovewherein

(a) the carrier has a specific surface greater than 15 m² per gram and aspecific pore volume greater than 0.1 cm³ per gram, and

(b) the halogen content, determined in the elemental form and based onthe total catalyst weight, is comprised between 0.3 and 3%, andpreferably between 0.6 and 2.3%.

Second preferred embodiments of the present invention involve the use ofthe catalysts defined above in the hydrorefining of petroleum fractionswhich contain less than 10 ppm, and preferably less than 1 ppm, byweight of sulfur, and whose boiling temperature at atmospheric pressureranges from 35° to 250° C.

Third preferred embodiments of the invention involve the use of thecatalysts in accordance with the invention in the isomerization ofhydrocarbons in the presence of hydrogen.

The carriers for the catalysts in accordance with the invention shouldbe refractory substances having an adequate specific surface and porevolume. The specific surface is comprised between 15 and 350 M² /g, andpreferably between 100 and 350 m² /g, and the specific pore volume isgreater than 0.1 cm³ g. The substances should, moreover, have a more orless pronounced acidic character since the isomerization reactions areknown to take place on acid sites. Alumina and aluminosilicates, forexample, are well suited for the fabrication of these carriers.

The most advantageous catalysts are those whose platinum-group metalcontent is comprised between 0.02 and 2%, based on the total catalystweight. To obtain satisfactory catalytic properties, the content of saidmetal is preferably greater than 0.10%; however, for reasons of catalystcost, it is preferably not higher than 0.70%.

The tin content, based on the total catalyst weight, is comprisedbetween 0.02 and 2% since below 0.02% and above 2% the improvement incatalytic properties over a catalyst containing only platinum isnegligible.

The applicants have further found that the most efficacious contents arethose comprised between 0.05 and 0.60%.

The halogen content may be comprised between 0.3 and 3%, and preferablybetween 0.6 and 2.3%, based on the total catalyst weight. The halogenpresent in the catalysts in accordance with the invention is preferablychlorine. It may be introduced into the catalyst composition in a mannerknown in the art, for example, during the preparation of the carrier, orduring the deposition of the metallic elements, by the use of solutionsof metal chlorides, for example.

The content of a metal M2 from groups Ia and IIa is such that the ratioM2/M1 of the number of atoms of the metal M2 to the number of atoms ofthe metal M1 from the platinum groups is comprised between 0.2 and 10,and preferably between 0.5 and 5. When the ratio is less, the yield ofhigh-octane effluent is not improved; and with higher ratios thestability of the catalyst diminishes.

The applicants have thus produced catalysts wherein the metal M2 issodium, lithium, potassium, calcium or barium.

The catalysts in accordance with the invention may be prepared byconventional procedures for impregnation of the carrier with solutionscontaining the elements to be deposited.

The impregnation of the carrier may be carried out:

(a) With at least one solution containing the three elements to bedeposited; or

(b) with at least two solutions, one containing two of the elements tobe deposited, the other the third; or

(c) with at least three solutions, each containing one of the elementsto be deposited.

The deposition of the metals may be carried out from solutions ofsoluble compounds of these metals, such as hexachloroplatinic acid,stannous chloride or the chloride of the metal from groups Ia and IIa.

The tin is preferably deposited before the platinum-group metal.

When the metals are not deposited simultaneously, the solid obtained maybe calcined between depositions at a temperature which in the case oftin is comprised between 400° and 700° C. and is preferably 600° C. orless, said calcination temperature being under 600° C. in the case ofthe platinum-group metals and under 550° C. in the case of platinum. Inthe case of the metals of groups Ia and IIa, the calcination temperatureis under 600° C.

When all of the metals have been deposited, the solid obtained iscalcined at a temperature of less than 550° C. Before this calcination,and after the last deposition, the halogen content of said solid may beadjusted by known means, such as an oxychlorination treatment.

The acidity of the carrier may be altered by an acid treatment withhydrochloric acid, for example, before the deposition of the elements,during the deposition or between depositions when the latter are notsimultaneous.

The catalysts in accordance with the invention may be used in thehydrotreatment of hydrocarbon charges.

They are particularly well suited for use in processes for thehydroreforming of petroleum fractions intended for the manufacture ofhigh-octane gasolines as well as in processes for the isomerization ofaromatic hydrocarbons.

The catalyst may be activated prior to the hydrotreatment by reductionwith hydrogen.

The activity of the catalyst may be maintained during the hydrotreatmentby adding a soluble hydrogenated compound (a chlorine, for example) tothe charge. It may also be advantageous to presulfurize the catalystwith a sulfurized hydrogen stream, for example, in order to minimize thecracking reactions which tend to occur at the start of the treatment.

The hydroreforming operation is carried out under the followingconditions:

Temperature: From 450° to 600° C.

Pressure: From 5 to 50 bars.

Molar ratio of hydrogen to hydrocarbons: From 2 to 10.

Hourly space velocity of charge (volume of gas passing over a unitvolume of catalyst per hour): From 0.5 to 5.

The hydroreforming process using the catalysts in accordance with theinvention may, in particular, be of the so-called "regenerative" type inwhich a portion of the catalyst is continuously withdrawn from thereactor, continuously regenerated by burning off the carbon formed withoxygen, either diluted or undiluted, and continuously recycled to thereactor after activation by reduction with hydrogen.

The isomerization of aromatic hydrocarbons is carried out under thefollowing operation conditions:

Temperature: From 300° to 600° C.

Pressure: From 5 to 50 bars.

Molar ratio of hydrogen to hydrocarbons: From 2 to 20.

Hourly space velocity of charge (as defined above): From 0.5 to 5.

As will be shown in the examples which follow, and which are in no wiselimitative, the applicants have obtained highly satisfactory resultswith various catalysts in accordance with the invention.

Example 1 relates to the preparation of catalysts in accordance with theinvention and of control catalysts.

Example 2 relates to the use of catalysts in accordance with theinvention and of control catalysts in the hydroreforming of a charge ofnormal heptane.

The nature of said charge does not constitute a limitation of the fieldof use of said catalysts since such a charge is generally used to testthe performance of hydroreforming catalysts. The results obtained maytherefore be extended to the case where the charge is a fractionintended for the manufacture of high-octane gasoline whose boilingtemperature ranges from 35° to 250° C. and whose sulfur content is lessthan 10 ppm, and preferably less than 1 ppm.

Example 3 relates to the isomerization of a charge formed by a mixtureof ethylbenzene, xylenes and toluene.

EXAMPLE 1

This example relates to the preparation, from a starting alumina, of:

(1) A control catalyst T consisting of platinum, tin and alumina andcontaining less than 100 ppm of sodium, this very small amount of sodiumstemming presumably from the starting alumina and from the water used inits preparation.

(2) Catalysts A1, A2, A3, A4, A5, B, C, D and E, consisting of platinum,tin and alumina and containing in addition more than 100 ppm of a metalfrom group Ia or IIa, introduced into the catalyst in accordance with amethod of preparation which will be described further on.

The starting alumina used is in the form of extrudates having thefollowing characteristics:

    ______________________________________                                        Average diameter of extrusions:                                                                     1.5 mm                                                  Specific surface:     190 m.sup.2 /g                                          Pore volume:          0.51 cm.sup.3 /g                                        Chlorine content (as measured                                                                       0.5% by weight                                          by x-ray fluorescence):                                                                             of the alumina                                          ______________________________________                                    

This alumina is calcined for 4 hours at 600° C. It will form the carrierfor the catalysts prepared and tested in this example and willhereinafter be referred to as carrier alumina.

PREPARATION OF CONTROL CATALYST T

100 g of starting alumina is immersed in 250 cm³ of an aqueous solutioncontaining 7 cm³ of hydrochloric acid and 7 cm³ of nitric acid which iscirculated over the alumina for half an hour.

A second solution containing 0.380 g of stannous chloride, SnCl₂.2H₂ O,10 cm³ of hydrochloric acid and 10 cm³ of water is then added to thefirst solution. The resulting solution is circulated for 2 hours.

After draining, the solid obtained is immersed in 80 cm³ of water, whichis circulated for 2 hours.

After renewed draining, the solid obtained is immersed in 120 cm³ of asolution of hexachloroplatinic acid containing 3 g/l of platinum. Thissolution is circulated for 4 hours.

After draining, the alumina is dried for 1 hour at 120° C., thencalcined at 530° C. for 2 hours.

The composition of the catalyst T so obtained is as follows:

    ______________________________________                                               Platinum, wt. % 0.40                                                          Tin, wt. %      0.21                                                          Chlorine, wt. % 0.98                                                          Sodium, ppm     58                                                     ______________________________________                                    

PREPARATION OF CATALYSTS A1, A2, A3, A4, A5, B, C, D and E

The catalysts A1, A2, A3, A4, A5, B, C, D and E are prepared like thecatalyst T up to the calcination step at 530° C. following thedeposition of the platinum.

100 g of the solid obtained is then placed in a rotary evaporator with250 cm³ of a chloride solution of a metal from group Ia or IIa ofvariable concentration. The composition of the solutions is given inTable I which follows.

                  TABLE I                                                         ______________________________________                                                   Chloride      Concentration                                        Catalyst   solution of   g/l                                                  ______________________________________                                        A1         Sodium        0.132                                                A2         Sodium        0.538                                                A3         Sodium        0.843                                                A4         Sodium        0.884                                                A5         Sodium        1.493                                                B          Potassium     0.917                                                C          Lithium       0.274                                                D          Calcium       1.554                                                E          Barium        3.344                                                ______________________________________                                    

After evaporation, the solids are dried for 18 hours at 120° C. and thencalcined for 2 hours at 530° C.

The chlorine content is adjusted by means of an oxychlorinationtreatment.

Catalysts A1, A2, A3, A4, A5, B, C, D and E are thus obtained whosecompositions are given in Table II below.

                  TABLE II                                                        ______________________________________                                                           Metal from group                                                              Ia or IIa                                                  Cata- Platinum  Tin     Chlorine        Content                               lyst  Wt. %     Wt. %   Wt. %  Kind     ppm                                   ______________________________________                                        A1    0.40      0.21    0.89   Sodium   130                                   A2    0.40      0.21    0.89   Sodium   530                                   A3    0.40      0.21    2.15   Sodium   830                                   A4    0.40      0.21    0.97   Sodium   870                                   A5    0.40      0.21    1.06   Sodium   1470                                  B     0.40      0.21    0.87   Potassium                                                                              1200                                  C     0.40      0.21    0.90   Lithium  150                                   D     0.40      0.21    0.87   Calcium  1400                                  E     0.40      0.21    0.89   Barium   5500                                  ______________________________________                                    

EXAMPLE 2

This example relates to catalytic tests run in the hydroreforming of acharge of normal heptane with the catalysts prepared in example 1.

25 cm³ of catalyst is placed in a stainless-steel reactor. A stream ofpure, dry hydrogen is then passed over the catalyst for 2 hours, thetemperature of the catalyst being maintained at about 500° C., and thepressure in the reactor being maintained at 7 bars. The chargeconsisting of normal heptane is then introduced at an hourly spacevelocity of 2 and a ratio of moles of hydrogen introduced to moles ofnormal heptane introduced of 5.

The tests are run at a fixed octane number, that is to say, as soon as adecrease in octane number is observed, the reactor temperature is raisedin order to bring the octane number to the level originally selected,which in this example is 103.

Samples taken from the reactor effluent permit determination of both thecomposition of the effluent and the equivalent octane number of theliquid by application to the chromatographic analyses of the ASTM blendnumbers appearing on the graphs with which those skilled in the art arefamiliar.

The variation of the reactor temperature as a function of time closelyresembles a straight line whose gradient is measured. The milder thegradient of that straight line, the better the catalyst, as thetemperature then needs to be adjusted but very slightly in the course oftime to secure the desired octane number. The time which it takes toreach the limit temperature of use then is extended, which is a decidedadvantage in industrial applications.

The results of these tests are presented in Table III which follows.

                  TABLE III                                                       ______________________________________                                                              Average                                                              Average  hydrogen        Temperature                                          C.sub.5 +*                                                                             yield  Initial  gradient as                                  Cata-   yield    (ltr/- temperature                                                                            a function                              Test lyst    Wt. %    ltr/)**                                                                              °C.                                                                             of time                                 ______________________________________                                        T1   T       59.5     227.9  509.4    0.073                                   A11   A1     59.7     219.0  512.6    0.090                                   A21   A2     61.2     223.8  516.5    0.073                                   A41   A4     62.2     251.2  522.9    0.100                                   A51   A5     63.8     276.7  536.3    0.151                                   B11  B       63.1     270.5  539.1    0.243                                   C11  C       61.0     232.2  526.1    0.095                                   D11  D       63.3     264.7  542.1    0.125                                   E11  E       64.5     287.9  547.7    0.162                                   ______________________________________                                         *C.sub.5 +: Hydrocarbons having 5 or more carbon atoms, including aromati     hydrocarbons. This figure is particularly representative of the yield         obtained with the catalyst as these hydrocarbons have a high octane           number.                                                                       **ltr/ltr: Liters of hydrogen/liter of charge, as measured under normal       conditions. This figure is also representative of the yield as the            hydrogen is obtained through dehydrogenation and dehydrocyclization           reactions.                                                               

It is apparent from this table that the C₅ + and hydrogen yields arehigher when metals from group Ia or IIa are present in a larger amountthan in the control catalyst, which demonstrates the superiority of thecatalysts in accordance with the invention.

EXAMPLE 3

This test relates to the isomerization of a charge consisting of amixture of ethylbenzene, xylenes and toluene with the aid of catalyst A3in accordance with the invention.

20 cm³ of catalyst A3 is placed in a stainless-steel reactor. A streamof pure, dry hydrogen is then passed over the catalyst for 2 hours, thetemperature of the catalyst being maintained at 500° C. and the pressurein the reactor being maintained at 22 bars. After the temperature hasbeen reduced to 480° C., the charge is introduced, which has thefollowing composition, in weight percent:

    ______________________________________                                               Toluene         1.08                                                          Ethylbenzene    26.15                                                         Paraxylene      2.34                                                          Metaxylene      68.19                                                         Orthoxylene     2.23                                                   ______________________________________                                    

The charge is introduced at an hourly space velocity of 2 and a ratio ofmoles of hydrogen introduced to moles of hydrocarbons of 7.5.

Samples are taken from the effluent after 191/2, 23 and 261/4 hours. Thecondensed liquid effluent is analyzed by chromatography.

The results are presented in Table IV which follows.

                                      TABLE IV                                    __________________________________________________________________________    Time                        191/2 h                                                                           23 h                                                                              261/4 h                                   __________________________________________________________________________    Yield in liquid products, % 100 96.80                                                                             97.63                                     Composition of                                                                         Liquid                                                                              Uncondensed                                                    effluent, wt. %                                                                        products                                                                            light hydrocarbons                                                                         0   3.20                                                                              2.37                                                     Hydrocarbons having                                                           from 1 to 4 carbons                                                                        0   0.11                                                                              0.06                                                     Hydrocarbons having                                                           5 carbon atoms                                                                             0   0.14                                                                              0.09                                                     Hydrocarbons other than                                                       benzene having 6 carbons                                                                   0   0.18                                                                              0.08                                                     Benzene      0.31                                                                              0.74                                                                              0.70                                                     Hydrocarbons other than                                                       toluene having 7 carbons                                                                   0.05                                                                              0.38                                                                              0.38                                                     Toluene      2.10                                                                              3.21                                                                              3.24                                                     Hydrocarbons other than                                                       xylenes and ethylbenzene                                                      having 8 carbon atoms                                                                      0.92                                                                              0.53                                                                              0.45                                                     Ethylbenzene 21.12                                                                             17.80                                                                             18.26                                                    Paraxylene   14.01                                                                             16.74                                                                             15.99                                                    Metaxylene   50.22                                                                             43.03                                                                             44.40                                                    Orthoxylene  11.27                                                                             13.94                                                                             13.98                                     Ethylbenzene conversion     19.24                                                                             31.93                                                                             30.17                                      ##STR1##                   1.038                                                                             1.013                                                                             1.022                                     __________________________________________________________________________

It is apparent from this table that the catalysts in accordance with theinvention are good isomerization catalysts, the ratio (xylenes atoutlet)/(xylenes at inlet) being high, which demonstrates that a largeportion of the converted ethylbenzene is in the form of xylenes.

We claim:
 1. In a catalyst for the hydrotreatment of hydrocarbons whichcomprises:a refractory oxide-mineral carrier; a halogen element, presentin combined form; and, in free or combined form,(a) from 0.02 to 2%,based on the total weight of the catalyst, of at least one metal M1 fromthe platinum group, and (b) from 0.02 to 2%, based on the total catalystweight, of tin, the improvement in said catalyst wherein it comprises incombined form, at least one metal M2 selected from groups Ia and IIa ofthe periodic table of the elements in such an amount that the ratioM2/M1 of the number of atoms of the metal M2 to the number of atoms ofthe metal M1 is such that 0.2≦M2/M1≦10.
 2. A hydrotreating catalystaccording to claim 1, wherein said carrier has a specific surfacegreater than 15 m² /g and a specific pore volume greater than 0.1 cm³/g, its halogen content is comprised between 0.3 and 3%, based on thetotal weight of the catalyst, and the platinum-group metal is platinum.3. A hydrotreating catalyst according to claim 2, wherein the halogencontained in the catalyst is chlorine.
 4. A hydrotreating catalystaccording to claim 3, wherein the carrier is an alumina whose surfacearea is comprised between 15 and 350 m² /g.
 5. A hydrotreating catalystaccording to claim 4, wherein the platinum content is from 0.1 to 0.7%,the tin content is from 0.05 to 0.06%, the chlorine content is between0.6 and 2.3%, the surface area of the carrier is between 100 and 350 M²/g, and the M2/M1 ratio is from 0.5 to
 5. 6. A catalyst according toclaim 2, characterized in that the metal M2 is sodium.
 7. A catalystaccording to claim 2, characterized in that the metal M2 is lithium. 8.A catalyst according to claim 2, characterized in that the metal M2 ispotassium.
 9. A catalyst according to claim 2, characterized in that themetal M2 is calcium.
 10. A catalyst according to claim 2, characterizedin that the metal M2 is barium.
 11. A hydrotreating catalyst accordingto one of claims 6 to 10, prepared by a procedure comprising at leastone impregnation of the porous carrier with at least one solutioncontaining at least one element selected from the group consisting oftin, the metals of groups Ia and IIa, and the platinum-group metals. 12.A catalyst according to claim 11, wherein said carrier is calcinedbetween individual depositions at a temperature whichin the case of tinis comprised between 400° and 700° C.; in the case of platinum is under550° C.; in the case of the other platinum-group metals is under 600°C.; and in the case of the metals of groups Ia and IIa is under 600° C.